Single Network Slice Selection Assistance Information

In Release 15, the S-NSSAI function was newly introduced to enable network slice selection for PDN connections in EPS, including those established over ePDG, and to handle slice continuity during mobility between EPS and 5GS. This included procedures for including an S-NSSAI received in EPS within the Requested NSSAI upon inter-system change to 5GS, and for establishing a NAS signalling connection due to changes in network slicing information. The release also introduced mechanisms for conveying S-NSSAI via extended PCO and for handling the PDU session ID during this inter-system mobility.

• S-NSSAI of a PDN connection context vie (e)PCO TS 24.008CR3116
• Handling of S-NSSAI and PDU session ID during mobility between EPS and 5GS TS 24.301CR2965
• Mode selection for inter-system change between EPS and 5GS TS 24.301CR2979
• Ciphering keys delivery for broadcast of ciphered assistance data TS 24.301CR3041
• Update of UE identity used for attach in S1 mode for single-registered UE without N26 TS 24.301CR3070
• Clarification on usage of ePDG selection procedures TS 24.302CR0662

+ 206 more changes

In Release 16, the S-NSSAI function was enhanced with the introduction of Slice-Specific Authentication and Authorisation. Furthermore, the release added new capabilities for network slice optimization based on VAL server policy and for network slice adaptation for VAL applications. These enhancements provided more granular control and optimization of network slices for vertical applications.

• CIoT Introduction of CN Selection and Steering TS 23.501CR0896
• Description of solution 2 in 23.725 for redundancy as an informational annex TS 23.501CR0754
• ATSSS-SMF and UPF selection TS 23.501CR0761
• Trusted non-3GPP Access Network Selection TS 23.501CR0783
• eSBA communication schemas related to general discovery and selection TS 23.501CR0799
• eSBA communication schemas related to UDM and UDR discovery and selection TS 23.501CR0800

+ 366 more changes

In Release 17, the S-NSSAI function was enhanced to support network slice restriction and optimization based on analytics from the NWDAF. It also introduced new capabilities for network slice adaptation for VAL applications by guiding updates to URSP rules and enabled coordinated resource optimization across multiple slices, including PNI-NPN slices. Furthermore, the release added support for predictive slice modification in edge deployments to maintain service performance during migration.

• Support of different slices over different Non 3GPP access TS 23.501CR2525
• Network Slice restriction based on NWDAF analytics TS 23.501CR2567
• NWDAF discovery and selection TS 23.501CR2575
• NWDAF discovery and selection based on provided ML models TS 23.501CR2585
• UP path selection enhancement based on analytics info provided by NWDAF TS 23.501CR2586
• NWDAF discovery and selection for model sharing TS 23.501CR2614

+ 402 more changes

In Release 18, key enhancements for S-NSSAI included the introduction of a **Partially Allowed NSSAI** and **Partially Rejected S-NSSAI** to provide finer granularity in slice admission control. The release also introduced the capability for **Alternative S-NSSAI replacement determined by NSSF** and added support for **graceful network slice PDU sessions release** during slice decommissioning or replacement. Furthermore, optimizations were specified for the support of **time validity policies for a network slice**.

• N3IWF selection enhancement for support of S-NSSAI needed by UE TS 23.501CR3707
• Discovery and Selection of the NWDAF Supporting Federated Learning in 5GC TS 23.501CR3772
• KI#4 23.501 AF traffic influence for common EAS, DNAI selection TS 23.501CR3788
• Common EAS/DNAI selection by AF TS 23.501CR3789
• Change of Network Slice instance for PDU sessions TS 23.501CR3867
• Introduction of 5GS Information Exposure TS 23.501CR3887

+ 557 more changes

In Release 19, enhancements to the S-NSSAI function focused on improving the Network Slice Capability Enablement (NSCE) service for vertical applications. Specifically, new procedures were introduced for **slice requirement verification and alignment** and for **network slice allocation within a Network Slice as a Service (NSaaS) model**. These additions provided improved policy harmonization between verticals and operators and enabled more dynamic slice lifecycle management based on VAL server policies.

• Enhancements to Network slice allocation procedure in NSaaS model TS 23.435CR0004
• Enhancements to Slice requirement verification and alignment capability TS 23.435CR0005
• Enhancements to Slice requirement verification and alignment capability TS 23.435CR0017
• Enhancements to Slice requirement verification and alignment capability TS 23.435CR0022
• RVAS with target NF selection enhancement. TS 23.501CR5364
• NF discovery and selection by target PLMN TS 23.501CR5399

+ 317 more changes

In Release 20, the S-NSSAI-related enhancements introduced new network slice capability enablement (NSCE) services for vertical applications, such as network slice optimization based on VAL server policy and predictive slice modification in edge deployments. These capabilities enable application-layer lifecycle management and coordinated resource optimization across multiple slices based on collected performance and analytics. Furthermore, the release introduced functionality for network slice adaptation for VAL applications, providing guidance to update URSP rules when a UE is subscribed to multiple slices.

• N3IWF/TNGF reselection considering energy related information. TS 23.501CR6493
• KI#1: Per UE application ranking related information exposed by EIF TS 23.501CR6501
• Energy Consumption information exposure and policy control TS 23.501CR6508
• SMF and PCF Selection for UIA_ARC TS 23.501CR6504